A variety of membrane filtration systems are known and many of these use pressurised systems operating at high transmembrane pressures (TMP) to produce effective filtering and high filtrate flux. These systems are highly effective but are also expensive to produce, operate and maintain. Simpler systems using membrane arrays freely mounted vertically in a tank and using suction applied to the fibre lumens to produce TMP have also been developed, however, these systems have been found in the past to be less effective than the pressurised systems.
Examples of such known systems are illustrated in U.S. Pat. No. 5,192,456 to Ishida et al, U.S. Pat. No. 5,248,424 to Cote et al and WO 97/06880 to Zenon Environmental Inc.
Recent developments have used combinations of gas scouring and backwashing in non-pressurised submerged membrane systems to improve operating efficiency. Many of these systems require complex and expensive manifolding to provide the required delivery/removal of liquids and gas at various stages of the process. The configuration and footprint of modules has also become important to many users of such systems.